The present invention refers to a method and an apparatus for manufacturing a fiber fleece by a fiber web producing means and a fleece laying machine, which is forming a cross lapped fleece web from a single or multi-layered fiber web continuously output by the fiber web producing means, said cross lapped fleece web having a thickness varying over the laying width.
A methods and an apparatus of this type are known from DE 43 04 988 C1. The aim of them is to generate a cross lapped fleece web having a uneven thickness profile when seen transversely to the fleece web direction, in that the thickness of the web is smaller in the rim portions than in the center of the web. The reason for this is that during the treatment of the fleece web in a needling machine, the fleece web is laterally drawing-in by the needling process, i.e. it becomes narrower, whereas at the same time the thickness profile changes. From a fleece web having an regular thickness and supplied to the needling machine, the latter generates a felt web being thicker on its rim portions than in its center. In order to eliminate this irregularity, a cross lapped fleece web supplied to the needling machine has a thickness profile in the transverse direction of the web which, starting from the center, becomes gradually smaller towards the rim portions of the web.
Different methods exist how a fleece web can be generated from a fiber web output by a carding machine, said fleece web seen in cross section transversely to the longitudinal extension of the web has an irregular thickness profile of the aforementioned kind. DE 40 10 174 A1 describes a fleece laying apparatus in which a temporary storage is formed in the nonwoven by de-coupling the movement of the laying carriage with respect to the nonwoven suppliers, said storage enabling a variable nonwoven deposition at the outlet of the fleece laying apparatus onto an outlet belt. Within a movement cycle of the fleece laying machine with forward and backward motion of the laying carriage, the fleece laying machine lays as much nonwoven as it is supplied during the same time by the nonwoven producing means. However, it is possible within the laying cycle to let more or less nonwoven emerge at the laying carriage. The mechanical effort and the control effort of such a fleece laying machine is, however, enormous.
DE43 04988 C1 describes a method in which the nonwoven is expanded or upset by a controlled uniform raising or lowering of the speed level of the drives conducting the nonwoven in the fleece laying machine compared to the output speed of the nonwoven producing means. The nonwoven exiting from a carding machine is running at constant speed over a supply belt driven at constant speed to the fleece laying machine whose nonwoven intake speed is varied depending on the movements of the laying carriage of the machine. This leads to a cyclic tensioning and a cyclic upsetting of the nonwoven web entering the fleece laying machine with resulting thinnings and thickenings of the nonwoven. However, only the cyclic timing of the generation of thickenings and thinnings in the nonwoven is fixedly coupled with the motion of the laying carriage. The local cycle or repeating of the thickenings and thinnings in the nonwoven is not defined in the same manner, since the portions at which thickenings and thinnings are produced are not unambiguously defined by the type of device. The tension produced by the drawing action is effective in the entire portion of the nonwoven lying on the supply belt between the carding machine and the fleece laying machine, and is especially effective at locations where thin portions are already existent in the nonwoven. Thus, it is not guaranteed that the thin portions are deposited by the fleece laying apparatus exactly at locations on the output belt where they should be deposited.
A method is known from FR 2 794 475 A1, in which depending on the cross sectional profile of a laid fleece web or a felt manufactured therefrom, the carding machine arranged in front of the fleece laying machine is controlled to generate a nonwoven web with distributed thin and thick portions. The disadvantage of this procedure is that it must be acted on relatively large moved masses, which requires high power control and drive means.
It is the object of the present invention to provide a method of the above-mentioned kind and a device suitable for performing same, which allow the deposition of a fleece web of a desired cross sectional profile.
To solve this object, the invention provides a method of manufacturing a fiber fleece by means of a nonwoven producing means and a fleece laying apparatus, which produces a fleece web from a single or multi-layered nonwoven web continuously supplied with a constant supply speed by the nonwoven producing means, said fleece web having a thickness variable across a laying width, in which method an intake speed at which the fleece laying apparatus accepts the nonwoven web is constant and the nonwoven web is longitudinally drawn in a drawing process on its way between the nonwoven producing means and the fleece laying machine cyclically in adaptation to laying movements of the fleece laying machine, wherein before or after the drawing process or before and after the drawing process a buffering of the nonwoven web takes place to adapt fluctuations of the nonwoven web speed caused by the drawing process to the supply and intake speeds of the nonwoven producing means and of the fleece laying machine, respectively.
A device according to the invention for manufacturing a fiber fleece from a nonwoven web, which is continuously output by a nonwoven producing means and supplied to a fleece laying machine, provides that the fleece laying machine is driven at a constant nonwoven intake speed, that a controllable drawing equipment is arranged between the nonwoven producing means and the fleece laying machine, through which said drawing equipment the nonwoven web is passed, said drawing equipment being adapted to draw the nonwoven web in the longitudinal direction, and that means are provided which depending on the laying movements of the fleece laying machine act on the drawing equipment in the sense of a cyclic change of the drawing effect exerted onto the nonwoven web, and that buffer storage means are provided, which are arranged between the drawing equipment on the one hand and the fleece laying machine or the nonwoven producing means on the other hand, or between the drawing equipment on the one hand and both of the fleece laying machine and the nonwoven producing means on the other hand.
Thus, the invention provides that a drawing process between the nonwoven production and the passing-on of the nonwoven web to the fleece laying machine is carried out at a defined location in the transport path of the nonwoven web, in practical application in a separate drawing equipment, which does not only lead to the generation of thick and thin portions in the nonwoven web at predetermined repeatings, but which also enables both units contiguous to the drawing equipment to run at constant speeds. In this case the speed modulation that the cyclically operating drawing equipment generates in the nonwoven web is buffered by buffer or temporary storage means with respect to the units disposed upstream and downstream of said drawing equipment.
When in the drawing equipment the intake-sided roller of the drawing equipment rotates at constant speed corresponding to the constant output speed of the nonwoven producing means and the cyclic drawing is generated by cyclic acceleration and delay of the rotational speed of the outlet-sided roller of the drawing equipment, a buffer storing on the outlet side of the drawing equipment is provided which cyclically accommodates a partial section of variable length of the nonwoven web. If on the other hand the outlet-sided roller of the drawing equipment is driven at constant speed according to the constant nonwoven intake speed of the fleece laying machine and if the drawing process is carried out by cyclic braking and re-accelerating the inlet-sided roller of the drawing equipment, a buffer storing between the nonwoven producing means and the drawing equipment is provided. A combination of both is also possible.
According to an alternative embodiment, the use of a buffer storage can be dispensed with, if the units contiguous to the drawing equipment are driven at the same speeds as the adjoining rollers of the drawing equipment. This requires a corresponding modulation of the output speed of the carding machine or of the intake speed of the fleece laying machine.
According to a further alternative of the invention a buffer storage is provided between the drawing equipment and the fleece laying machine, and the fleece laying machine operates at a nonwoven intake speed that depends on the laying movements of its laying carriage. The aim of such a measure shall briefly be discussed here.
The laying carriage of a fleece laying machine carries out a reciprocating movement extending transversely to the laying belt on which the fleece web is produced by cross-lapped depositing the nonwoven. The reversal of movement at the end of each movement stroke is not carried out suddenly but during controlled braking and acceleration phases. If the nonwoven web is supplied at constant speed, thickenings in the deposited fleece web result due to these braking and acceleration phases exactly where the fleece web is actually to be thinner. Thus, known fleece laying machines are constructed in a manner that the laying carriage has a variable nonwoven transport speed, which requires the use of a buffer storage to synchronize the regular nonwoven intake speed of the supply belt of the fleece laying machine with the variable nonwoven transport speed of its laying carriage.
If the nonwoven intake speed of the supply belt is adapted to the nonwoven transport speed of the laying carriage, a buffer storage in the fleece laying machine can be renounced. The required buffer storing is performed according to this embodiment of the invention by the buffer storage provided between the drawing equipment and the fleece laying machine, said buffer storage being required for the compensation of the cyclically variable output speed of the drawing equipment anyway. If the buffer storage operates by using a movable storage roller or a reciprocating, continuously rotating nonwoven storage belt, the movement drive thereof must be controlled in accordance with the demands of the fleece laying machine and those of the drawing equipment.
The drawing equipment may be a multi-stage drawing equipment, wherein buffer storages may be arranged between the individual stages, said buffer storages allowing a relaxation of the nonwoven fibers that is advantageous in certain applications.
It is further advantageous if the working result is measured, and a feedback control of the drawing equipment is carried out on the basis thereof. For this purpose is the fleece web thickness detected transversely to the longitudinal extension of the fleece web, e.g. by the aid of radiometric, acoustic, optical or mechanical measuring means, and the output signals of these measuring means are used for affecting the drawing extent and the length of the drawing zones within the nonwoven web.